The present invention concerns oil-soluble molybdenum complexes of polyol ester dispersants, their method of preparation, and the utility of oil-soluble molybdenum polyol ester dispersants as lubricating oil additives, which markedly improve the friction-reducing properties of lubricating oils employed for crankcase lubrication of internal combustion engines.
There are two principle environments which are encountered by automotive crankcase lubricants, i.e. cyclical high and low temperatures from stop-and-go driving and continuous high temperatures from extended operation of the automobile over long distances. Each of these environments provokes the presence in the lubricant of varying proportions of foreign particles such as dirt, soot, water and decomposition products resulting from breakdown of the oil. This foreign matter appears responsible for the deposition of a mayonnaise-like sludge which circulates with the oil.
During the past decade, ashless sludge dispersants have become increasingly important, primarily in improving the performance of lubricants in keeping the engine clean of deposits and permitting extended crankcase oil drain periods while avoiding the undesirable environmental impact of the earlier used metal-containing additives. One commercial type of ashless dispersant involves esters of alkenyl substituted acids, e.g. polyisobutenyl succinic acids, with polyols e.g., pentaerythritol, as taught in U.S. Pat. No. 3,381,022; however, such dispersants often-times contain olefinic unsaturation making them susceptible to oxidative degradation especially under high severity conditions such as elevated oil temperatures and extended drain intervals.
A second type of ester dispersant involves chloro lactone ester dispersants prepared via the esterification of alkenyl chloro lactone acids with pentaerythritol as taught in U.S. Pat. No. 3,755,173; however, the inherent propensity of such dispersants, or antirust compounds as taught in U.S. Pat. No. 2,279,688 towards elimination of corrosive HCl to give unsaturated products, can promote decomposition of the hydrocarbon lubricant, corrode metal engine parts, and promoter varnish deposition on the internal surfaces of the engine.
In the operation of an internal combustion engine, there are many "Boundary Lubrication" conditions where two rubbing surfaces must be lubricated, or otherwise protected, so as to prevent wear and to insure continued movement. Moreover, where, as in most cases, friction between the two surfaces will increase the power required to effect movement and where the movement is an integral part of an energy conversion system, it is most desirable to effect the lubrication in a manner which will minimize this friction and/or reduce wear. As is also well known, both wear and friction can be reduced, with various degrees of success, through the addition of a suitable additive or combination thereof, to a natural or synthetic lubricant. Similarly, continued movement can be insured, again with varying degrees of success, through the addition of one or more appropriate additives.
While there are many known lubricant additives which may be classified as antiwear, antifrication and extreme pressure agents and some may in fact satisfy more than one of these functions as well as provide other useful functions but rarely if ever dispersancy, it is also known that many of these additives act in a different physical or chemical manner and often compete with one another, e.g. they may compete for the surface of the moving metal parts which are subjected to lubrication. Accordingly, extreme care must be exercised in the selection of these additives to insure compatibility and effectiveness.
Known ways to solve the problem of energy losses due to high friction in crankcase lubrication include the use of synthetic ester base oils which are expensive and the use of insoluble molybdenum sulfide and graphite dispersions which have the disadvantage of giving the oil composition a black or hazy appearance. It would be desirable then to provide oil-soluble molybdenum compounds and thus overcome the disadvantage. Oil-soluble molybdenum additives taught as useful in lubricating oils include: colloidal molybdenum complexes in combination with dispersants (see U.S. Pat. No. 3,223,625); the reaction product of molybdenum ions and hydrocarbon-substituted succinic anhydride-alkylene polyamines carried out in oil and a cosolvent such as water, tetrahydrofuran and dimethylformamide (see U.S. Pat. No. 3,652,616); and oil-soluble molybdenum containing succinimides (see translation of Khimiya i Teknologuja Topliv i Masel, No. 6 pp 49-51 of June 1978 having article entitled "Antioxidant Efficiency and Mechanism of Antioxidant Action of Metal-Containing Dispersant Additives").
The practical exploitation of various types of molybdenum compounds and complexes as lubricant additives has been hindred not only by their insolubility and/or corrosiveness but also by their synthetic accessibility.
While it is known that molybdenum compounds can be reacted with low molecular weight aliphatic alcohols or glycols (see U.K. Pat. No. 967,838) and with alcohols (see U.S. Pat. Nos. 2,805,997 and 2,987,478), it would be desirable to design molybdenum complexes of high molecular weight polyol ester dispersants to enhance the lubricity of oils and fuels to which said esters are added.
It is an object of this invention to overcome the related disadvantages and shortcomings of the prior art materials.